The present invention relates to a process for making non-combustible carbonized cellulosic material, and more particularly to non-combustible carbon filters made of such material and to smoking articles which contain such filters.
The use of carbonized matter as a filter or filtration enhancer and as a partial or total substitute for the customary tobacco shred content of a cigarette have been reported, as have various methods of manufacturing such filters and cigarettes.
U.S. Pat. No. 4,219,031 discloses a smoking product having a central, porous, combustible core of carbonized matter circumscribed by tobacco shreds. The core is produced by pyrolyzing a rod of loosely twisted, or substantially non-woven, cellulosic material which has been treated with an additive for ash control to produce a carbonized rod consisting of at least about 80% carbon. The ash control additive may be Na.sub.2 B.sub.4 O.sub.7, CaCl.sub.2 or K.sub.4 Fe(CN).sub.6.
Commonly assigned, co-pending U.S. application Ser. No. 296,233, filed Aug. 25, 1981, discloses a method of making a combustible carbonized rod for use in a smoking product. According to the method disclosed, a cellulose rod comprising a coherent bundle of cellulosic paper made by the wet paper-making process, and which contains a binding agent and an additive selected from the group of compounds consisting of Na.sub.2 B.sub.4 O.sub.7, CaCl.sub.2, K.sub.4 Fe(CN).sub.6, Al.sub.2 (SO.sub.4).sub.3 and Cu.sub.3 SO.sub.4, and mixtures thereof, is pyrolyzed. The binding agent is preferably one or more of the aforementioned additives, and thus the rod is preferably formed using the additive as the binding agent. The resultant carbonized rods are employed as filters in smoking products either alone or in addition to a conventional filter, such as a cellulose acetate filter, and exhibit properties of filtration which are superior to those of conventional cellulose acetate filters.